One method of waste gas treatment whereby noxious (gas) ingredients such as SO.sub.2 and NO.sub.x are removed from waste gases is a method wherein waste gas is irradiated with electron beams to form various active species such as O and OH radicals from oxygen, water, etc. in the waste gas so that the active species act on the noxious (gas) ingredients in the waste gas such as to form mist and this mist is further changed into dust in the presence of ammonia or the like, the mist and dust then being captured with a dust collector or the like.
FIG. 1 schematically shows the structure of an electron beam irradiation portion of a waste gas treatment apparatus for carrying out this waste gas treatment method. As illustrated, a waste gas duct 1 is provided with irradiation windows 2, and waste gas passing through the waste gas duct 1 is directly irradiated with electron beams 4 emitted from electron beam accelerators 3 through the irradiation window 2. In the structure wherein the electron beams 4 are directly applied to the inside of the waste gas duct 1, when the amount of waste gas increases to that which would be treated in a practical application and the size of the waste gas duct 1 increases correspondingly, it has heretofore been necessary, in order to allow all of the waste gas to absorb the electron beams 4, to dispose a multiplicity of electron beam accelerators 3 (two in the illustrated example) at the outer periphery of the waste gas duct 1 and also to increase the maximum range of the electron beams 4, as shown by the chain lines 5. However, disposition of a multiplicity of electron beam accelerators 3 involves disadvantage in that the structure of the waste gas treating apparatus becomes complicated and costs are raised. Further, in order to increase the maximum range of the electron beams 4, it is necessary to raise the acceleration voltage for electron beams, which leads to a substantial rise in the cost of the electron beam accelerators 3. In addition, if electron beams are accelerated at high voltages, high-energy X-rays are generated and a thick concrete wall or the like must be provided in order to provide shielding from such high-energy X-rays, which results in a rise in the overall cost of the waste gas treatment apparatus. Thus, the prior art suffers from various problems.
It should be noted that there are techniques which aim to have all of the waste gas irradiated with electron beams at a uniform dose, including those disclosed in the specifications of Japanese Patent Public Disclosure Nos. 49-096975 and 55-097232 and U.S. Pat. Nos. 4,507,265 and 4,596,642, but none of them completely solves the above-described problems.
Further, there is a technique disclosed in the specification of Japanese Patent Public Disclosure No. 61-68126 wherein atmospheric air is introduced into an electron beam irradiation reactor to allow said air to be irradiated with electron beams to thereby form ozone and oxygen atoms therein. Said air having ozone and oxygen atoms is mixed with a waste gas to oxidize NO in the waste gas to form NO.sub.2 and then the waste gas is introduced to a wet absorption tower to effect desulfurization and denitration.
In the desulfurization and denitration of that technique, since a wet absorption tower is used the absorbing solution used in the wet absorption tower contains a large amount of nitrogen and sulfur compounds which are difficult to treat and costly waste water disposal equipment is therefore needed to treat the absorbing solution. This leads to the problem of high costs in the installation and maintenance thereof.
The present invention is directed to solution of the above-described problems of the prior art and it is an object of the present invention to provide a method of and apparatus for treating waste gas by irradiation with electron beams, wherein a part of the waste gas taken from the main stream of waste gas is irradiated with electron beams using a low-voltage type accelerator to form active species such as O and OH radicals in the irradiated waste gas and to thereby activate it, the activated waste gas then being uniformly fed into the main stream of waste gas and thereby effectively removing noxious gas ingredients such as SO.sub.2 and NO.sub.x from the waste gas.